1. Field of the Invention
The present invention relates to an apparatus and method for supporting plural video codecs.
2. Discussion of the Background Art
Communication environment at present and in future is and will be rapidly changing enough to break distinction between wired coverage and wireless coverage, or boundaries of nations. Especially, the third generation communication environment classified by IMT-2000 shows a current tendency in mobile communications, providing users with not only image and voice but also diverse information comprehensively or in real time mode.
Development in personal communication system also made it possible for cellular phones or PCS possible to extend services from a simple voice communication to transmission of mobile text messages, wireless Internet access, and transmission of moving pictures that are usually seen in TVs through a personal communication terminal.
Such technique is being an essential element in a digital television system, which processes moving images to digital data, transmits/receives the digital data in real time mode and displays on a screen, and in a personal communication terminal adopting IMT-2000, which transmits moving images in real time mode.
Traditionally, a portable terminal was devised to transmit/receive human voices only. However, thanks to the development of multimedia and digital data processing techniques, it is now possible to transmit various information including voice and image.
Most of all, commercial use of the above technique largely contributes to a compression technique for moving pictures which applies special digital processing to analog image signals, e.g., quantization and variable length coding, transmits the digitized signals over a transmit digital channel, and decodes the image signals at a receiving terminal, thereby transmitting more information at a higher transmission speed.
Therefore, unlike in the past, a moving image communication terminal provides a higher-level service to users by enabling the users to listen and see real-time moving images and voices.
FIG. 1 is a schematic block diagram illustrating a configuration of a related art video decoder.
Referring to FIG. 1, the video decoder includes a VLD (variable length decoder) 100, an IQ (inverse quantization) unit 110, an IDCT (inverse discrete cosine transformation) unit 120, a MC (motion compensation) unit 140, and a mixing unit 130.
The VLD (variable length decoder) 100 decodes transmitted compressed bit stream to reconstruct an image therefrom, and transmits decoded signals to the IQ unit 100.
Then the IQ unit 110 performs a quantization process to the transmitted signal from the VLD 100, in an inverse way from a compression method in an encoder for reconstruction of the image.
The IDCT unit 120 performs an inverse discrete cosine transformation process on the transmitted signal from the IQ unit 110.
The mixing unit 130 determines whether an image frame of the transmitted signal from the IDCT unit 120 is an intra mode image that starts first or an inter mode image with a previous image frame. If the image frame of the transmitted signal turns out to be the intra mode image, the mixing unit 130 outputs the image right away since there is no motion vector therein.
The MC unit 140 obtains a difference between a motion vector of an image frame currently being decoded and of a previous image frame, and compensates the decoded image.
An operation of the video decoder having the above video codec will be now explained below.
An analog image signal undergoes discrete cosine transformation and quantization in an encoder, and an image frame signal whose variable length is coded is transmitted to the decoder in a compressed bit stream.
The decoder transmits the transmitted bit stream to the VLD 100, and the VLD 100 transforms value and length of the transmitted bit stream to a two dimensional code.
Then the VLD 100 transmits the two-dimensional code signal to the IQ unit 110.
The IQ unit 110 performs the inverse scan and inverse quantization to the transmitted signal from the VLD 100, and transmits the signal to the IDCT unit 120.
The IDCT unit 120 performs the inverse discrete cosine transformation to the transmitted signal from the IQ unit 110. Then the image signal is inputted to the mixing unit 130. The mixing unit 130 determines whether this image frame to be reconstructed is an intra mode image that starts first or an inter mode image having a previous image frame, and if the image frame is of the intra mode image, outputs the image right away since there is no motion vector therein. Finally, the MC unit 140 obtains a difference between the motion vector of the image frame to be decoded and of the previous image frame, and compensates the decoded image.
To compare various types of video codecs, some codecs have the same operation block function and the same embodiment for each codec, but some codecs have the same function yet a different embodiment for each codec. For example, IDCT unit 120 performs the inverse conversion, and its embodiment is equal in MPEG4 and H.263 video codecs. However, although IQ unit 110 performs the inverse quantization, its embodiment is different in MPEG4 and H.263 video codecs.
Therefore, a problem arises that imaging equipment should have several built-in video codecs to support various kinds of video, which only increases size and cost of the imaging equipment.